The World War II codebreaking station at Bletchley is well known and its activities documented in detail. Its decryption capabilities were vital to the war effort, significantly aiding the Allied victory. But where did the messages being deciphered come from in the first place? This is the extraordinary untold story of the Y service, a secret even more closely guarded than Bletchley Park. 'Y service' was the code for the chain of wireless intercept stations around Britain and all over the world. Hundreds of wireless operators, many of them civilians, listened to German, Italian and Japanese radio networks and meticulously logged everything they heard. Some messages were then used tactically but most were sent on to Station X -- Bletchley Park -- where they were deciphered, translated and consolidated to build a comprehensive overview of the enemy's movements and intentions.